Transfemoral Socket Design and Muscle Function

The objective of this pilot research project is to evaluate the effect of prosthetic socket design on amputated limb hip muscle strength and endurance in Service members, Veterans, and civilians who use above-the-knee prostheses. Traditional above-the-knee socket designs provide pelvic support that interferes with hip motion. They may also reduce the effort required from amputated limb hip muscles to stabilize the hip and amputated limb, risking further loss of muscle mass and strength beyond that due to amputation. Long-standing use of above-the-knee sockets with pelvic support may therefore intensify amputated limb muscle loss and weakness, leading to challenges with walking and balance, increasing the effort required to walk, and contributing to degenerative changes in the hips and knees. Alternative socket designs that lessen the loss of muscle mass and strength are therefore required. The investigators have developed a new socket without pelvic support for above-the-knee prosthesis users called the Northwestern University Flexible Sub-Ischial Suction (NU-FlexSIS) Socket. This new socket design increases user comfort and is often preferred by users over sockets with pelvic support. This new socket does not lessen the mechanical function of the socket, or walking and balance performance. Our recent research suggests that walking with this new socket may also increase amputated limb hip muscle size. However, more research is needed to demonstrate that this new socket design improves amputated limb hip muscle strength and endurance, leading to better function. A socket design that increases amputated limb hip muscle strength and endurance would provide a simple way to restore amputated limb hip muscle weakness in above-the-knee prosthesis users. Despite a considerable decrease in hip muscle size and strength due to amputation surgery, amputated limb hip muscles are expected to compensate for the loss of knee and ankle function by providing stability and propulsion during walking. Walking in the new socket design without pelvic support is expected to increase amputated limb hip muscle strength and endurance, providing an appealing alternative to traditional resistance training in order to retain hip muscle strength. Unlike traditional resistance training, using this new socket design would not require additional time or equipment, and may be effective just by walking in the home, community, or workplace. Due to existing infrastructure (e.g., ongoing clinical adoption of the NU-FlexSIS Socket, existing instructional materials and courses for fabrication and fitting of the NU-FlexSIS Socket, as well as a continuing partnership with Chicago's largest provider of prosthetic clinical care), the investigators anticipate being able to translate our research results to clinical practice by the end of the project period. The investigators expect the results of the proposed pilot research project to directly and positively benefit the health and well-being of Service members, Veterans, and civilians who are above-the-knee prosthesis users. Benefits of increasing amputated limb hip muscle strength and endurance may include: i) improved control over the prosthesis, ii) better balance, iii) reduced effort to walk, and iv) protection against joint degeneration. For Service members these benefits could improve their performance on challenging and/or uneven ground, and increase the distance and speed they can walk or run. For Veterans, these benefits could lead to greater independence during activities of daily living, and fewer falls, reducing the physical and emotional burden on family members and caregivers.

Inclusion Criteria: worn an ischial containment socket for ≥ 2 years, able to walk short distances (10 meters), ability to read, write, and speak English, ≥ 2 years using a liner-based suspension, and a residual limb length ≥ 5". Exclusion Criteria: amputation of a second leg, contralateral complications (e.g., hip replacement), or other major neuromusculoskeletal or cardiovascular conditions (e.g., heart failure).